1. Field of the Invention
This invention relates to a magnetic display system which utilizes coatings of microcapsules containing light-absorptive magnetic particles and light-reflective non-magnetic particles in a dispersing oily medium and interchanges each cluster of the particles' position within the individual microcapsules for absorption or reflection of light to thereby form a contrast image of brightness and darkness.
2. Description of the Prior Art
As prior art concerning magnetic display systems, there is one in which a transparent plastic sheet is formed over the entire surface with honeycomb-like cavities, each with a dimension of about 2 mm as one side and depth. Each cavity is filled with white a pigment liquid and magnetic particles and is sealed with a transparent sheet to prevent leakage of the filling matter. In this case, a rod-like permanent magnet is shifted over the entire display surface from one end of the back surface of the magnetic display plate to the other, thus bringing magnetic particles in each honeycomb-like cavity toward the back side of the display plate and leaving the white color of the white pigment on the front surface. By moving a rod-like magnetic pen with its writing end in contact with the white surface of the display, magnetic particles in the scribed area are brought to the front surface, thus forming an image.
Another magnetic display system is known which utilizes a non-magnetic substrate coated with a layer of microcapsules containing magnetic particles, and a permanent magnet as a means to form and erase an image.
Of these prior art magnetic display systems, the former forms an image with a shift of magnetic particles in honeycomb-like cavities from the back surface to the front surface. Thus, it is impossible to obtain an image resolution sharper than the cavity size. In addition, the provision of a mold for forming the honeycomb-like cavity and the step of sealing the white pigment dispersed in liquid together with magnetic particles can not be readily attained. Further, it is technically substantially impossible to make a display board providing honeycomb-like cavities in a size as large as a blackboard. Further, it is technically extremely difficult to seal the white pigment dispersed in liquid together with magnetic particles in honeycomb-like cavities provided over the entire surface of such large size display. Further, it is also not easy to provide a small-size display, like a pocket-size display, due to the construction noted above. Therefore, the former display system can find only limited applications. At any rate, for formation of an image the total amount of magnetic particles in each honeycomb-like cavity are shifted from the back surface to the front surface, and therefore it is impossible to form a sharp image. Besides, when the display board is held vertically for a lengthy time, after formation of an image, magnetic particles in the honeycomb-like cavity tend to sink to the bottom thereof. Further, it is difficult to provide a display board having a free size.
The latter magnetic display system is far superior to the former display system with the white pigment and magnetic particles dispersed in liquid sealed in a honeycomb-like cavity of a plastic molding in that the quality of images that can be formed is very superior, the polarity orientation of magnetic particles can be changed with a very slight magnetic flux density and a display having a desired size can be readily obtained. However, this system requires magnetic particles of nickel, or alloys thereof, capable of providing a surface gloss and having a flakier shape (i.e., a flat and elongated shape) than those of ferrite or ordinary iron oxide obtainable by mass production, as well as readily capable of polarization, because it is necessary to provide a strong contrast between light absorption when the particles are orientated vertically and light reflection when the particles are orientated horizontally. This leads to increased costs.